This invention relates generally to cathodic protection systems, and particularly, to impressed current cathodic protection systems.
In order to protect varied metal structures, such as pipelines, power cables, underground transformers, etc., it is a common practice to use cathodic protection systems. One type of cathodic protection system is called an impressed current system and operates by neutralizing the galvanic current produced in the burial medium, usually the ground, and the structure to be protected. One type of impressed current system is known as a rectifier-ground bed installation. In a common type of rectifier-ground bed installation, an external source of potential is provided to a buried anode, via an existing AC power supply (although the power can be provided via other means, such as, for example, gas driven generators, etc.). Coupled to the AC power supply is a rectifier whose positive terminal is connected to a string of anodes, which are referred to as the ground bed, and which are buried adjacent the structure bed. The negative terminal of the rectifier is connected to the structure. In common practice, the anodes of the ground bed can be connected in any number of configurations, e.g., series, parallel, etc., and are commonly formed of various materials, such as graphite, carbon, silicon, iron, etc.
The efficacy of ground bed systems is a function of the resistivity of the soil in which the anodes are buried, the number of anodes, the spacing between anodes, the distance to the buried structure, etc. For example, the higher the ground resistivity, the greater the number of anodes required to cover a desired area. Inasmuch as the resistivity of the soil is usually lower at greater depths, it is a common practice to dispose the anodes at substantial depth, e.g., 100 or more feet, below the surface. At such depths, the soil tends to be less resistive due to its compositional makeup and/or the presence of water. Depending upon the application, deep bed anodes can be disposed at depths from 100 feet (30.5 m) to 800 feet (244 m) or more, with 150 feet (45.8 m) being average.
Various deep anode bed systems have been disclosed in the patent literature. For example, in U.S. Pat. No. 3,725,669 (Tatum), there is disclosed an impressed current, deep anode bed, cathodic protection system. That system makes use of a long tube extending down the bore hole and in which tube one or more anodes are suspended. The bore hole is filled with a granular, electrically conductive material, e.g., coke breeze, so that the current from the anode spreads out radially therefrom.
While the system of the Tatum patent appears generally suitable for its intended purposes, it is somewhat complex in structure and provides only limited means for the replacement of any of its anodes in the event of anode failure or preventive maintenance.
Likewise, prior art deep anode bed cathodic protection systems in general, also suffer from various disadvantages, such as complexity, cost, ability to replace anodes expeditiously, etc.
To that end, a preferred type of deep anode assembly having an anode and conductors constructed to be readily replaceable after being installed within the bore hole was invented and is disclosed and claimed in co-inventor William Schutt's co-pending U.S. patent application Ser. No. 293,900 filed on Aug. 18, 1981, whose disclosure is incorporated by reference herein. That assembly shall be referred to hereinafter as a replaceable deep anode assembly.
The replaceable deep anode assembly disclosed and claimed in the above mentioned co-pending patent application is installed within a deep bore hole by connecting together successive sections of conduit as the assembly is lowered into the bore hole. While this method is satisfactory from a functional standpoint, it is clearly desirable to provide a means for facilitating the installation of a deep anode assembly.